(1) Field of the Invention
This invention relates in general to a float chamber for carburetors and, in more particular, to an inner air vent system for maintaining the float chamber under a positive pressure relative to the throat of the carburetor venturi.
(2) Description of the Prior Art
In the prior art, various types of float chambers for carburetors have been developed and used. In basic carburetor designs, the float chamber is connected through a fuel passage to the fuel jet located in the venturi of the carburetor for delivery of fuel to the engine. The fuel in the float chamber is maintained at a constant level, with the tip of the fuel jet being held to stand slightly above the float chamber fuel level maintaining a level difference enough to allow the controlled discharge of fuel, but without spilling, from the fuel jet where a slight vacuum is created by the air flow through the venturi. Thus, float chambers are provided with air vents to admit atmospheric air into the space above the fuel in the float chamber.
Some of the conventional float chambers are equipped with an outer vent, as represented by the art proposed in Japanese laid-open utility model application No. 57-43071, that directly opens into the top space of the float chamber exposing the fuel to atmospheric air. These float chamber structures have been found to have the disadvantage of permitting entrance of foreign matter into the float chamber with the influx of air.
To eliminate the above-mentioned difficulty, various improvements have so far been developed. One such an example is an inner air vent system which consists of an air passage having its one end opened into the air space in the top of the closed float chamber and its other end connected to the air intake pipe for the carburetor to admit air, cleaned by the air cleaner, into the float chamber, as taught in Japanese published patent application No. 60-33991.
There has recently been increasing demand on the development of a smaller, more lightweight engine. However, minituarization has somewhat been discouraged by the modern inner air vent carburetor designs that the air intake pipes are located to stand close to the top portion of the float chambers making it rather impossible to insure a required difference of height between the fuel level in the float chamber and the opened tip of the air passages for proper fuel discharge. Furthermore, where the vehicle has to be operated on an extremely rough surface or run on a steep slope, the conventional techniques are altogether incapable of preventing gravitational flush of fuel from the float chamber into the carburetor venturi through the air vent passage due to the inclined engine body resulting in abnormal combustion in the cylinders.
The present invention has been proposed to eliminate these difficulties of the prior art inner air vent float chambers.